1. Field of the Invention
This invention relates to an image filing apparatus for filing image signals on an optical disk, constructing an image retrieval data base on a fixed magnetic disk, and carrying out image retrieval on the basis of the image retrieval data base.
2. Description of the Prior Art
Many medical images have heretofore been utilized for medical treatment or research in, for example, medical facilities such as hospitals. Most of the medical images are radiation images. In recent years, many computed tomography (CT) images, magnetic resonance (MR) images and the like are also utilized.
The medical images should be stored for investigating changes in diseases or injuries of patients, and it is legally stipulated that the medical images be stored for a predetermined period. Therefore, in hospitals or the like, the number of stored medical images increases from day to day. The medical images have heretofore been stored in the form of hard copies. However, storage as hard copies requires a large storage space and burdensome operations for control and retrieval of the medical images in hospitals or the like.
Accordingly, in recent years, it has been proposed to employ an electronic filing method in which medical images are retrievably filed as image signals on a recording medium such as an optical disk. In the case where the medical images are filed in this manner on the recording medium, the space requirement and the burden of image storage are reduced, and the operation of image retrieval becomes easy and quick.
In an image filing apparatus for filing the image signals in the manner as mentioned above, image retrieval signals corresponding to the image signals representing each medical image are filed to construct a data base, and image retrieval is carried out using the data base.
The amount of the image signals representing each medical image is very large, and therefore an optical disk having a very large recording capacity is generally used as the recording medium for filing the image signals. On the other hand, as the recording medium for filing the image retrieval signals corresponding to the image signals representing each medical image, it is advantageous to use a magnetic disk that has a recording capacity smaller than the recording capacity of the optical disk and is suitable for quick retrieval. In this manner, the number of the images capable of being filed on a single optical disk can be increased up to, for example, at least 1,000, and on the other hand, the image retrieval speed can be increased substantially. Also, though the recording capacity of the magnetic disk is smaller than the recording capacity of the optical disk, the amount of the image retrieval signals which are to be filed on the magnetic disk is very much smaller than the amount of the image signals which are to be filed on the optical disk, the image retrieval signals for at least 1,000,000 images for example can be filed on the magnetic disk.
Since it would take several years even in a large hospital before the amount of the image retrieval signals filed on the magnetic disk reaches a value corresponding to 1,000,000 images, a single magnetic disk can be used for that long a period without replacement.
However, fixed magnetic disks readily break when handled incorrectly. Therefore, it may often occur that the magnetic disk breaks in the course of long-term use. If the magnetic disk having the image retrieval signals stored thereon breaks, the image retrieval data base which has been constructed on the magnetic disk is lost. In such a case, even though the image signals are stored on the optical disk, it becomes impossible to re-output the image by retrieval of the image signals, and therefore the image filing apparatus becomes substantially inoperable.
On the other hand, in the course of constructing the image retrieval data base over a long period, it may be required to re-construct a more efficient data base by collecting only specific signals, for example, signals for a specific subject of diagnosis and a specific period. However, such a requirement cannot be satisfied with the data base constructed on the magnetic disk in the manner as mentioned above since the data base is formed by merely storing all the image retrieval signals.
Besides the case of the filing of medical images, the same problems arise in the case where the magnetic disk is used continuously for a long period and an image retrieval data base is constructed on the magnetic disk.